Filming type corrosion inhibitor for steam and condensate lines



United States Patent FIUMING TYPE CORROSION INHIBITOR FOR STEAM AND CONDENSATE LINES Wayne L. Denman, Oak Park, and Chih Ming Hwa, Chicago, Ill., assignors to Dearborn 'Chemical Company, Chicago, 11]., a corporation No Drawing. Application November 14, 1956 Serial No. 622,009

11 Claims. ('Cl. 212.7)

The present invention is directed to the prevention or inhibition of corrosion caused by steam and steam condensate in steam generating systems.

The present invention is applicable to water systems generally, which include systems such as steam boiler systems, steam return condensate systems, steam distribution systems, heat transfer water systems, evaporator systems, processing water systems, cooling water systems, and the like.

A considerable amount of research work has been done in preventing corrosion in the aforementioned systems by employing what is known as a filming type inhibitor. In theory, the filming type inhibitor forms an extremely thin film, normally measured in terms of molecular units, on the surfaces to be protected and thereby insulates the cathodic or anodic surfaces which are believed to be responsible for initiating corrosion.

The present invention provides corrosion inhibiting compounds which can be introduced with the steam line or directly into the boiler and are carried over with the steam to form protective insulating films on the metallic surfaces to be protected.

An object of the present invention is to provide an improved method for inhibiting corrosion on metallic surfaces subjected to the corrosive action of a steam condensate. 3 p

A further object of the invention is to provide'an improved process for securing a thin film of a corrosion inhibitor on metallic surfaces subjected to the corrosive action ofa steam condensate. i A further object of the invention is to provide a process for inhibiting corrosion on metallic surfaces which employs, extremely small amounts of the corrosion inhibitor. A further object 'of the invention is to provide improved corrosion inhibiting compounds from materials which'are readilyavailable commercially.

We have now found that certain heterocyclic'nitrogen compounds have a very pronounced a'bility'to inhibit corrosion caused bysteam condensates. The compounds of the present invention have the general formula:

where X is the remainder of aheterocyclic nitrogen ring, said ring containing a total 'of two nitrogen atoms and from. 3 to.4. carbon atoms (i.e., the remainder of an imida zoline or a hydro-pyrimidine group), one of the radicalsrRand R',is eithera hydrogen atom orashort "chain p'olar; .group, and the other of the said radicals i's'fan'aliphatic grdupcontaining from 11 to 17 carbon atoms.

i; The imidazoline compounds coming Within the scope H .2 of the present invention may .be represented by the fol lowing formula:

R'N \N H|,-,JJH where Rand R have the same difinitions as previously given. T

Hz-AZH;

(2) l-hydroxyethyl 2-heptadecenyl imidazoline (3) l-hydroxycthyl Z-heptadecyl imidazoline n as HOCHzCHP Ego-CH2 (4) l-aminoethyl 2 -heptadecyl imidazoline j i V. '1 V" I "G nHai V (5) l-hydroxymethyl 2-pentadecyl imidazoline m si HOCHPN/ \N (6) l-hydroxymethyl 2-tridecy1 imidazoline (7) l-hydroxyethyl Z-undecylJimidazolinc Cn n The following-pyrimidine compounds can also be employed for the purposes of the invention:

(8) l-coco Z-methyl 4,5,6-trihydropyrimidine where R is the residue from coconut fatty acids.

9 l-tallow Z-hydroxyethyl 4,5,6-trihydropyrimidine where R is the residue-from .tallow fatty acids.

(10) l-tallow Z-aminoethyl 4,5,6-trihydropyrimidine l mc c-cmcmnm H. l

where R is the residue from tallow fatty acids.

(11) l-coco Z-butyl 4,5,6-trihydropyrimidine where R is the residue from coconut fatty acids.

(13) Pheptadecyl Z-heptadecenyl 4,5,6-trihydropyrimidine (14) l-heptadecyl Z-undecyl 4,5,6-trihydropyrimidine aime HgC fi-CnHn 4 (l5) Z-heptadecyl l,4,5,tS-Ietrahydropyrirnidine (16) Z-undecyl 1,4,5,6-tetrahydropyrimidine The compounds of the present invention represent balanced molecules which are capable of being adsorbed onto the metal surfaces to'insulate the metal from the corrosive action of the steam condensate. The films which are produced on the metal need not be continuous although the greater the continuity in the film, the more the corrosion inhibiting eifectiveness will be increased.

The compounds of the invention are polar-molecules which enable them to be attached to the metal surfaces. We have found that when employing com-pounds having shorter chain lengths thanindicated for the compounds of this invention, the compounds are too soluble and do not adsorb readily on the metal. At too high a chain length,- there is an association tendency betweenthe long chains, and a uniform protective film is not produced;

The imidazoline compounds of the'present invention can be conveniently prepared by reacting aliphatic 1,2- diamines alone or in admixture with their mineral acid salts with high molecular weight carboxylic acids at temperatures from 200 to 300 C. in the presence of a condensing agent such as aluminum chloride, phosphorus trichloride, stannic chloride, or. phosphorous pentoxide.

The compounds of the present invention vary widely as to their physical characteristics. The compound 1- hydroxyethyl 2-heptadecy1 imidizaoline is strongly cationic. An aqueous solution of this compound is alkaline, with the pH of a 1% dispersion in water being 8.9.

The compound 1-hydroxyethyl Z-hep-tadecyl imidazoline is fairly easy to disperse in water because of the presence of thehydroxyethyl group. Other imidazoline compounds are not so readily dispersible, however, and compounds such as 2-:heptadecyl imidazoline may be rendered more. dispersible by forming the acetate or the hydrochloride salt and dispersing the salt into the system. Under the conditions existing inthe boiler, the salt hydrolyzes and the acidic. component reacts, with sodium ions present in the boiler water. to form a sodiumsalt which remains in. the boiler while theimidazoline itself is steam distilled and forms a protective film of that compound on the metal surfaces of the steam lines.

The cyclic compounds may also be solubilized or dispersed by the addition of a condensate of ethylene oxide and octadecyl amine to the corrosion inhibitor composition. One such readily available condensate is sold under the name Ethomeen 18/60" and consists of the reaction-product of about 50 mols of ethylene oxide with I mol of technical grade, octadecyl amine. Generally, an amount ofsolubilizing agent ranging from about V3 to bi of they amount of the cycliccompound will be etfective to disperse the cyclic compound satisfactorily.

In addition to the amine condensate mentionedabove, other poly-alkoxy surface active compounds may be employed as dispersing-agents. Among these are the addition products of propylene oxide and ethylene oxide with ethylene diamine (Tetronics), propylene glycol-ethylene oxide condensation products (Pluronics) and polyoxyalkylene glycols (Ucons).

The compound 2-heptadecyl imidazoline acetate is marketed by Carbide and Carbon Chemicals Company under the trade mark Crag 341. This composition is sold as a 34% solution of the imidazoline acetate in isopropanol. The solution is readily soluble in cold water, and a 1% solution of the 2-heptadecyl imidazoline 'ace tate has a pH of 5.0.

The compound l-aminoethyl Z-heptadecyl imdazoline is prepared from a tallow fatty acid and diethylenetriamine. The compound is relatively insoluble in water, but may have its dispersibility characteristics increased by forming the acetate salt by reaction of the compound with glacial acetic acid at about 200 F. An aqueous solution of 1% concentration of the acetate has a pH value of 4.4.

The pyrimidine compounds are most conveniently prepared by cyclicizing an N-alkyltrimethylene diamine with a suitable acid at elevated temperatures. The following examples are typical of the procedure involved.

The compound l-heptadecyl 2-heptadecenyl 4,5,6,-trihydropyrimidine was prepared in the following manner. About 143 grams (0.357 mol) of heptadecyl propylenediamine (Duomeen T) and 100 grams (0.357 mol) of octadecenoic acid (Neo-Fat 94-04) were mixed in a 500 m1. three necked flask equipped with a stirrer, thermometer, and reflux condenser attached to a Dean-Stark trap. The mixture was heated at 282 to 305 C. for about two hours. During the heating, 12.4 grams of water were evolved. The final product weighed 227.7 grams, and had an acid number of zero. The free compound was insoluble in water, and so was employed in the form of its acetate salt.

Other trihydropyrimidine compounds are prepared in the same manner, substituting the appropriate amounts of difierent acids.

The compound 2-heptadecyl 1,4,5,6-tetrahydropyrimidine was prepared as follows. A mixture of 0.774 mol of stearic acid (Neo-Fat 18) and 0.774 molof trimethylene diamine with 70 ml. of benzene was heated at 103 to 123 C. for seven hours during which time 18 grams of water was removed by azeotropic distillation. The product was transferred to a distillation flask and the excess diamine was recovered. A white, solid undistilled residue remained. The final product analyzed 33.7% Z-heptadecyl 1,4,5,6-tetrahydropyrimidine and 66.3% 2-heptadecyl 1,4,5,6-tetrahydropyrimidine molecular complex with stearic acid. The complex was converted to the pyrimidine by treatment with dilute sodium hydroxide. The product was insoluble in water, and so was employed in the form of its acetate salt.

Other tetrahydropyrimidines are prepared in the same manner, with an appropriate change in acid.

A very convenient starting material for preparing pyrimidine compounds of the invention is the compound tallow trimethylene diamine which is a commercially available product being marketed by General Mills, Inc. under the trademark Diam 26. With a compound of this type, a short chain alkyl group may be added by heating the amine at temperatures in excess of about 200 C. with a fatty acid containing from about 2 to 5 carbon atoms per molecule.

The usual dosage amounts to about 1 to parts per million of the inhibitor based upon the weight of steam. However, in initiating the treatment cycle, particularly where the steam generating system has considerable amounts of corrosion or mill scale already present, it is desirable to cut down the dosage initially to about one half p.p.m. until some of the scale has been washed away, after which the dosage can be increased to the normal level of about 2 to 10 p.p.m. Amounts of the compound in excess of about 10 p.p.m. are not only wasteful from This compound has an amine number of 122.

the standpoint of economy, but frequently do not produce as good results as are obtained at the lower dosage levels.

The corrosion inhibiting effectiveness of the compounds was tested in the following manner. Test coupons were prepared from cold rolled, SAE-1009 mild steel. These coupons were immersed in the condensate receiving well of a pilot plant steam generating system. The dissolved oxygen and free carbon dioxide present in the condensate flowing from the receiving well were controlled at 1.5

10.5 p.p.m. and 45:5 p.p.m., respectively. The corrosion inhibitor was fed into the condensate at various dosages, and the weight loss ocurring in each coupon after various intervals of time was determined.

The following table summarizes the data obtained when the compound l-hydroxyethyl 2-heptadecyl imidazoline was fed at a concentration of 10 p.p.m.:

The following table presents the data obtained in the corrosion test when the compound Z-heptadecyl imidazoline acetate was fed at a concentration of 10 p.p.m.:

Table II Milligram loss per coupon The same corrosion test when applied to the compound l-aminoethyl 2-heptadecyl imidazoline acetate fed at a concentration of 10 p.p.m. produced the following results:

Period of time in days:

DQQ INH Table III Milligram loss Period of time in days: per coupon where X is the remainder of a heterocyclic nitrogen ring containing a total of two nitrogen atoms and from 3 to 4 carbon atoms, one of the radicals R and R is selected from the group consisting of hydrogen atoms and short chain polar groups, and the other of said radicals is an acyclic aliphatic hydrocarbon group containing 11 to 17 carbon atoms.

2. The method of claim 1 in-which the total number ofcarbon atoms in the radicalsR andR is at least 15.

3; The methodof clairrrl" in which the total number of'carbon atoms inrthe radicals R and R is 15 to 19.

4. The method'of claim lin which the total number of carbon atoms in the radicals R and R is 17'.

5. The methodof inhibiting corrosion on metallic surfaces subject to corrosion ,by a, steam condensate which comprises vaporizing and then forming a film of 2-h'eptadecyl irnidazoline on said surfaces by deposition from the steam to inhibit said corrosion.

6. The method of inhibiting corrosion on metallic surfaces subject to corrision by a steam condensate which comprises vaporizing and then forming a of l-hydroxyethyl Z-heptadecyl imidazoline on said surfaces by deposition from the steam to inhibit said'corrosion.

7. The method of inhibiting corrosion on metallic surfaces subject to corrosion by a steam condensate which comprises vaporizing and then forming afihnof'haminoethyl Z-heptadecylimidazoline onsaid surfapes by deposition from thesteam to, inhibit saidicorrpsion.

8. The method of, inhibiting steam, condensate-corrosionin a steam boiler system which comprises introducing into said system a compound selected, from the group consisting of, compoundshaving theformula:

where'X is the remainder of a heterocyclic nitrogen ring containing a total of two nitrogen atoms andtrom three to four carbon atoms, one of the radicals R and R is selected from the group consisting ofhydrogen atoms and short chain, polargrollps, and theotherot said radicals is an acyclic aliphatic hydrocarbongroup containing 11 to 17 carbon atoms, and hydrolyzable .saltsof. said compounds, vaporizing saidcompound insaid system and depositing said compound in said systemby deposition from the steam in amounts suflicient to form a corrosion inhibiting film in the portions of said system susceptible to steam condensate corrosion,

9. The method of inhibiting steam condensate corrosion in a steam system which comprises introducing into saidsystem the compound 2-heptadecyl imidazoline acetate, hydrolyzing said compound in said system, volatilizing'the compound dissociated from its salt into the steam, and depositing the dissociated compound in amounts sufficient to form a corrosion inhibiting film in the portions of said system susceptible to steam condensate corrosion.

10. The method of inhibiting steam condensate corrosion in a steam system which comprises vaporizing into said system the compound l-hydroxyethyl Z-heptadeeyl imidazoline in amounts sufiicient to form a corrosion inhibiting film in the portions of said system susceptible tosteam condensate corrosion, and depositing said compoundfrorn the steam in the form of a film on said portions.

11. The method of inhibiting steam condensate corrosionin a steam system which comprises introducing into said system the compound l-aminoethyl 2-heptadecyl imidazoline acetate, hydrolyzing said compound in said system, volatilizing the compound dissociated from its salt, and depositing the dissociated compound in amounts sufficient to form a corrosion inhibiting film in portions of said system susceptible to steam condensate corrosion.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,227 Blair et a1. May 9, 1950 2,562,571 Partridge July 31, 1951 2,582,138 Lane et al. Ian. 8, 1952 2,587,249 Ulmer Feb. 26, 1952 2,720,490 Oxford Oct. 11, 1955 2,771,417 Ryznar et al Nov. 20, 1956 FOREIGN PATENTS 528,579 Canada July 31, 1956 

1. THE METHOD OF INHIBITING CORROSION ON METALLIC SURFACES SUBJECT TO CORROSION BY A STEAM CONDENSATE WHICH COMPRISES VAPORIZING AND FORMING A FILM OF A COMPOUND ON SAID METALLIC SURFACES BY DISPOSITION FROM THE STEAM, WHICH FILM CONSISTS ESSENTIALLY OF A COMPOUND HAVING THE FORMULA: 